body {
    display: flex;
    justify-content: center;
    align-items: center;
}

form {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    width: 400px;
    height: 435px;
    background-color: #fff;
    border-radius: 10px;
    box-shadow: 0px 0px 10px rgba(0, 0, 0, 0.1);
}

.reg {
    width: 300px;
    height: 40px;
    line-height: 40px;
    margin-top: 10px;
}

#username, #password, #realName, #bookName, #bookType, #bookPrice, #bookWriter {
    width: 200px;
    height: 40px;
    line-height: 40px;
    text-indent: 20px;
}

label {
    position: relative;
    left: -10px;
}

.fill {
    width: 100px;
    height: 40px;
    line-height: 40px;
    background-color: beige;
    border: 1px solid grey;
    position: relative;
    top: 20px;
    font-size: 18px;
    font-weight: bold;
}

.readme {
    float: right;
    position: relative;
    left: 100px;
    top: 30px;
}

.logins a {
    color: grey;
}
.checkbox{
    margin-left: 20px;
    margin-top: 20px;
}
.checkbox input{
    width: 20px;
    margin-left: -5px;
}